1. Field of the Invention
The present invention relates to a keyswitch, and, more particularly, to a keyswitch that is suitable for use in an input device of, for example, a personal computer.
2. Description of the Related Art
As shown in FIGS. 9 and 10, a related keyswitch 21 used in an input device of, for example, a personal computer has a base 22 and first engagers 22a. The base 22 is disposed at the bottommost portion of the keyswitch 21 and is formed of a metallic plate, such as an aluminum plate. The first engagers 22a protrude from the illustrated right side of the base 22.
Each first engager 22a comprises two opposing engaging walls 22b and 22b, which are disposed on both sides of an engaging groove 22c. Second engagers 22d, which are disposed on the illustrated left side of the respective first engagers 22a, each have a slide groove 22e and have a substantially L shape. One side of each slide groove 22e is open.
As shown in FIG. 10, the first engagers 22a and the second engagers 22d vertically oppose the base 22.
A membrane switch 23, disposed on the base 22, comprises an upper sheet 23a, a lower sheet 23b, and a spacer 23c. A movable contact (not shown) on the lower surface of the upper sheet 23a opposes a stationary contact (not shown) on the upper surface of the lower sheet 23b. The spacer 23c is disposed between the sheets 23a and 23b. 
The membrane switch 23 has holes (not shown) for receiving the first engagers 22a and the second engagers 22d. The first engagers 22a and the second engagers 22d are inserted in the holes, and the membrane switch 23 is disposed on the base 22.
A first lever 24 and a second lever 25, which are combined in the form of a pantograph, are disposed on the membrane switch 23. As shown in FIG. 10, the first lever 24 has a U shape in plan view, and has a pair of opposing arms 24b, each having a first engaging protrusion 24a. 
As shown in FIG. 9, each arm 24b is disposed tilted leftward and upward, and has a second engaging protrusion 24c at the illustrated upper side thereof.
The arms 24b have respective bearings 24d that are disposed toward the respective first engaging protrusions 24a. 
As shown in FIG. 10, the second lever 25 has a substantially rectangular shape in plan view. It has first vertically protruding first bar-shaped engaging protrusions 25a and 25a on the illustrated right side thereof and second vertically protruding second bar-shaped engaging protrusions 25b and 25b on the illustrated left side thereof.
The second lever 25 has a circular hole 25c, disposed leftward in FIG. 10, for receiving a rubber spring 27 (described later). The rubber spring 27 is positioned at the circular hole 25c. 
Cylindrical bearings 25d and 25d, which can be fitted to the respective bearings 24d of the first lever 24, protrude from the upper and lower side surfaces of the second lever 25.
By fitting the bearings 25d of the second lever 25 to the bearings 24d of the first lever 24, as shown in FIG. 9, the first lever 24 and the second lever 25 are combined in the form of a pantograph.
The first engaging protrusions 24a of the first lever 24 are rotatably engagingly supported by the respective first engagers 22a of the base 22, and the second engaging protrusions 25b of the second lever 25 are slidably engagingly supported by the respective second engagers 22d of the base 22, so that the first lever 24 and the second lever 25 can move vertically.
A keytop 26 is supported at the top portions of the first lever 24 and the second lever 25. The keytop 26 has first engagers 26b on the illustrated right side of a back surface 26a. The first engaging protrusions 25a of the second lever 25 rotatably engage two engaging walls 26c and 26c of their respective first engagers 26b. 
In FIG. 9, second engagers 26d are disposed to the left of the first engagers 26b. The second engagers 26d each have a slide groove 26e, which is open on one side. The second engaging protrusions 24c of the first lever 54 slidably engage the slide grooves 26e. 
The rubber spring 27 for resiliently biasing the keytop 26 upward is disposed on substantially the central portion of the back surface 26a of the keytop 26. The rubber spring 27 is placed on the membrane switch 23 on the base 22 by being mounted thereto with an adhesive or the like.
The rubber spring 27 has a dome-shaped hollow 27a in the inner portion, and a protrusion 27b that protrudes downward from the ceiling defining the inner portion of the hollow 27a. 
A top end 27c of the rubber spring 27 is positioned on the back surface 26a of the keytop 26.
When the keytop 26 of the above-described related keyswitch 21 is pressed downward, the first lever 24 and the second lever 25, which are in the form of a pantograph, rotate, causing the keytop 26 in a horizontal state to move downward.
At the same time, the keytop 26 that has moved downward elastically deforms the rubber spring 27, so that the protrusion 27b in the hollow 27a moves downward. The protrusion 27b pushes the upper sheet 23a, so that the movable contact (not shown) comes into contact with the stationary contact (not shown) on the lower sheet 23b, as a result of which the membrane switch 23 is turned on.
Thereafter, when the keytop 26 is released, the keytop 26 returns to its initial upper position by the elastic force of the rubber spring 27, and the first lever 24 and the second lever 25 move upward. The upper sheet 23a of the membrane switch 23 returns to its initial state by its own restoring force, and moves out of contact with the lower sheet 23b, as a result of which the membrane switch 23 is turned off.
In such a related keyswitch 21, the keytop 26, which is supported by the pair of levers 24 and 25 that are combined in the form of a pantograph, moves vertically in a substantially horizontal state parallel to the base 22 regardless of what part of the keytop 26 is pressed.
Japanese Unexamined Patent Application Publication No. 12-148356 is a document for reference.
However, such a related keyswitch 21 has the problem of reduced assembly efficiency because the structure for supporting the first lever 24 and the second lever 25 in the form of a pantograph is complicated.
In addition, since the first lever 24 and the second lever 25 are combined in the form of a pantograph, the height of the related keyswitch 21 is increased, so that it is difficult to make it thin.